So instead of doing it the way Michael demonstarted I used loop cuts. I extruded the stair railings and at the top of the stairs and snapped it the the face. I had a small issues where the geometry was sanpping at a wierd position until I realized had loose geometry, so I made sure to remove any doubles and everything worked from there.
I used loop cuts too, its a lot easier. I guess theres more than one way to do something!